The removal of very fine dust, typically in the particle size range of about 0.3 to 20 microns, from industrial gases is a difficult and expensive operation to perform efficiently. Devises traditionally employed for this purpose involve electrostatic precipitation, bag houses and wet scrubbers. Larger particles are removed mostly by cyclone separators and gravity settlers.
Gravity settlers are among the least expensive air pollution control equipment but are effective usually only for the removal of particles having a particle size greater than 50 microns, then they can be removed by simple gravity separation.
A search conducted in the facilities of the U.S. Patent and Trademarks Office has located the following U.S. Patents as the most relevant:
______________________________________ 1,094,521 1,500,128 1,532,730 2,673,620 2,829,735 ______________________________________
All there prior patents show the provision of some form of filter for the removal of dust particles from gas streams.